Modern vehicles have installed therein a large number of electronic control units, referred to simply as “ECUs”. ECUs installed in a vehicle are communicably connected to each other via a communication bus, such as a CAN (Controller Area Network) bus, a LIN (Local Interconnect Network) bus, or the like to share data required for integral control of the vehicle and to carry out the integral control of the vehicle using the shared data.
Such conventional vehicle control systems including a large number of ECUs communicated with each other in a communication bus are disclosed as an example in the U.S. Pat. No. 6,438,462B1 corresponding to Japanese Examined Patent Publication No. 3343685.
The number of ECUs to be installed in a vehicle has increased as in-vehicle devices have become more sophisticated in functionality, and also it has increased in order to improve the safety of a vehicle. The more the number of ECUs to be installed in a vehicle increases, the more the number of ECUs to be connected to a communication bus installed in the vehicle increases.
The increase in the number of ECUs to be connected to a communication bus increases the length of a communication path between the communication bus and each ECU to be connected thereto. This may complicate communication path design between the ECUs and the communication bus in order to secure communication reliability, and therefore, make it difficult to secure communication reliability.
For addressing the problem, it is proposed to monolithically integrate, into one ECU, various functions required for vehicle control and conventionally implemented by several ECUs.
When various functions required for vehicle control are integrated into one ECU, it is proposed to design a new control circuit, such as a new microcomputer, capable of implementing all of the various functions by various pieces of software, and to install the newly designed control circuit into the one ECU.
However, this approach increases not only the cost of developing the various pieces of software, but also the processing load of the new control circuit significantly.
For meeting the increase in the processing load of the new control circuit, as the new control circuit, a high-performance microcomputer whose processing speed is faster than microcomputers that are installed as corresponding control circuits in the several ECUs is required to constitute the one ECU.
In addition, because the increase in the processing load of the new control circuit increases power consumption of the new control circuit, new measures are required against the increase in power consumption of the new control circuit. For example, measures for heatsinking are required to be taken against increase in heat due to the increase in power consumption of the new control circuit.
In view of the above descriptions, when various functions conventionally implemented by several ECUs are integrated into one ECU, it is preferable to install several control circuits respectively installed in the several ECUs into the one ECU; these several control circuits are designed to implement the various functions.
This approach can eliminate the need to design a new control circuit capable of implementing all of the various functions required for vehicle control, and can integrate the several ECUs using their existing control circuits. For these reasons, it is possible to relatively simply change the specifications of a vehicle control system using several ECUs at low cost.
Note that, because each of the several control units can implement a corresponding at least one of the various functions while communicating with another control unit, it individually includes a communication function.
Therefore, when several control circuits are installed in one ECU (integrated ECU), because of reducing the number of communication paths between the integrated ECU and a communication bus, it is preferably to couple the integrated ECU to the communication bus via a single transmission and reception route.
In order to couple the integrated ECU to the communication bus via the single transmission and reception route, a bus transceiver installed in the integrated ECU, which allows data communications with an external device via the communication bus, is made shareable among the several control circuits. For making the bus transceiver sharable among the several control circuits, it is possible to use a communication arbitration circuit for arbitrating access requests to the external device transmitted from the several control circuit. The communication arbitration circuit is disclosed as an example in the U.S. Pat. No. 5,812,880 corresponding to Japanese Examined Patent Publication No. 3346079.
In applying the communication arbitration circuit to arbitration of the access requests transmitted from the several control circuits, the communication arbitration circuit has functions of:
holding the access requests;
sequentially outputting, to the bus transceiver, the access requests;
holding data transmitted from the bus transceiver; and
outputting the held data to at least one of the control circuits designated as a target device by the held data.
However, this application of the arbitration circuit to arbitration of the access requests transmitted from the several control circuits may make it necessary for the arbitration circuit to provide a storage area for holding the access requests.
In addition, in order to improve high-speed communication required for vehicle control, it may be necessary for the arbitration circuit to provide a signal processing circuit capable of executing the arbitration task set forth above at high speed.